The present invention relates to microactuators having macroscopic force and displacement. More particularly, the invention relates to microactuators comprising a 3-D array of small actuator cells, which are formed from stacked substrate sheets having an electrode layer on only one side of the substrate sheet.
Most microactuator arrays, used as MEMS (Micro-Electro-Mechanical-Systems) devices, are fabricated in silicon. Despite the many favorable attributes of silicon, it is not always a suitable or ideal material for every application of MEMS. Silicon is brittle and subject to breaking, particularly as the total device size increases. This brittleness limits devices, especially actuators, to relatively small sizes capable of only small displacements and forces. The shapes that can be realized in silicon are typically restricted by crystalline planes or 2-D fabrication processes, and more complicated structures often result in prohibitively high cost and low yield. It would be of great advantage to the art if another material, other than silicon, could be used for MEMS and actuators. In particular, it would be advantageous if the structure used to fabricate the actuator required significantly fewer electrode layers with no substantial loss in force, while requiring less power to operate.
The present invention provides an electrostatic microactuator array device including a plurality of sheet pairs secured together over the sheet pair lengths and widths. The sheet pairs can be formed of a first sheet and a second sheet, wherein the first and second sheets have a front and back surface. The first and second sheets preferably have a substrate layer disposed toward the sheet back surface, a dielectric layer disposed toward the sheet front surface, and a conductive layer disposed between the substrate layer and the dielectric layer. Voltage applied to the conductive layers causes an attractive electrostatic force between the first and second sheets. The first and second sheet front surfaces are secured together at a number of spaced bonding locations along the sheet lengths and widths, such that the first and second sheets have a plurality of non-bonded regions between the bonding locations. In this configuration, the sheet pairs have outer surfaces formed of the back surfaces of the first and second sheets. The outer surfaces of the adjacent sheet pairs are secured together over the sheet pair lengths and widths to form an array of sheet pairs.
In one illustrative embodiment, the sheet pairs are bonded together along continuous bonded locations extending across the sheets. These bonded locations may be disposed along substantially straight lines or curved lines, as desired. Alternatively, the bonded locations may be a discontinuous series of spots or lines extending over the sheet surface.
The first and second sheets may lie substantially flat between the bonding regions, relying on an applied tension to the microactuator to separate the sheets. Alternatively, the sheet pairs may be pre-shaped to form cavities between the bonded regions, even with no applied tension to the microactuator. This latter configuration may be accomplished in any number of ways. For example, the first sheet may be curved, and the second sheet may be substantially flat. In this configuration, the first sheet undulates away from the second flat sheet between the bonded locations. In another example, both the first and second sheets may curve away from each other in the non-bonded regions, coming back together at the bonded locations. The curved or corrugated sheets may thus form cavities between the bonding regions even with no applied tension to the microactuator. In any event, it is contemplated that the sheet pairs may collectively be aligned substantially along a plane, or may conform to a curved surface.
The sheets included in the present invention require only a single electrode layer bonded or applied to a substrate layer. The electrode layer is preferably formed of a conductor material deposited over the substrate layer, and a dielectric material deposited over the conductor. The substrate layer may be a polymer, ceramic, silicon, steel, or any other material that provides the desired characteristics for a particular application. The first and second sheets of each pair can be bonded together so that the front surfaces of the sheets are in close proximity to one another near the bonded regions. The close proximity of the sheets helps overcome the initial separation of the non-bonded regions of the sheets, and zip together inward from the bonding locations toward the center of the non-bonded regions. The attraction of the sheets for each other upon the application of an electrical potential provides the force for the microactuator.
In one method of manufacture, the sheet pairs are formed by first bonding together the sheets at periodic intervals, for example, along regularly spaced parallel lines. This can be done using manufacturing techniques such as heat bonding or adhesive application. With the sheet pairs formed, the sheet pairs can be bonded together many at a time, to form the microactuator array. The process of bonding together the multiple, already formed sheet pairs can be less precise with little or no loss in device performance than the process used to bond the sheets of a sheet pair. Since no voltage is applied between the sheet pairs, the distance between the sheet pairs may not be as critical as the distance between the sheets forming each pair.